Convert decameter to nanometer

The in-between metric units are taught at school and then mostly forgotten – except regionally. Dutch motorways carry a 'hectometre post' every 100 m, so traffic news and breakdown services place a jam at 'A2, hectometre post 57.3'. In Sweden and Norway the decimetre is an everyday word, a half-decimetre being about two inches, and the decilitre does the same job in Nordic recipes. The decametre is the odd one out: 10 m is about the length of a bus, and the unit is hardly used anywhere.

Atoms and molecules are measured in ångströms, 0.1 nm: the Bohr radius of hydrogen is 0.53 Å, a carbon–carbon bond 1.54 Å, and X-rays have wavelengths of about 1 Å, which is why crystallographers keep the unit although it is not part of the SI (chemistry tables give the same radii in picometres, 53 pm). The nanometre is the scale of the DNA double helix (2 nm across), of viruses (20–300 nm) and of visible light (380–750 nm); a chip's '3 nm' process is a marketing name, its transistors are really tens of nanometres apart. Bacteria, red blood cells (7 µm) and hair (50–100 µm) belong to the micrometre, and the femtometre, or fermi, to the atomic nucleus: a proton is 1.7 fm across.